This application claims priority rights of and is based on Japanese Patent Application No. JPAP10-181486 filed on Jun. 12, 1998 in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a method and apparatus for image processing, and more particularly to a method and apparatus for image processing which is capable of converting a color image signal to a mono-chrome signal.
2. Discussion of the Background
Conventionally, mono-chrome image output machines such as, for example, a facsimile machine, a digital copying machine, a printer, and a mono-chrome display machine, have been provided with an image processing technique which subtracts and outputs a brightness signal when handling a color image signal. However, the brightness signal is insufficient to represent colors. For example, two colors which have the same brightness but different colors can not be represented by a single brightness signal.
Several different types of solution for this problem have been proposed. A first type of solution has been proposed by Japanese Laid-Open Patent Application Nos. 63-268659 (1988), 63-216747 (1988), 02-101497 (1990), 02-274178 (1990), and 02-243056 (1990). This solution uses a technique which converts each color to a corresponding hatching pattern in a predefined manner. A second type of solution which converts a color difference to a mono-chrome gray-scale is described in Japanese Laid-Open Patent Application No. 04-170866 (1992). A third type of solution by Japanese Laid-Open Patent Application No. 06-292006 (1994) uses a technique which produces a contour signal obtained by differentiating color signals and adds it to a brightness signal.
However, each of these solutions have its own problems. For example, the first and second types of solution are limited in the number of colors to express and the third type is too complex to handle. In addition, when a color signal is changed to a mono-chrome signal, it is generally required that a resolution of the color signal is changed.
Accordingly, an object of the present invention is to provide a novel image processing apparatus which can properly produce a mono-chrome image signal from a color image signal and freely change a resolution.
Another object of the present invention is to provide a novel method for image processing which can properly produce a mono-chrome image signal from a color image signal and freely change a resolution.
To achieve these and other objects, a novel image processing apparatus includes a converter which performs a frequency conversion operation on a color image signal which includes a brightness signal and color signals and divides values of each of the brightness signal and the color signals into high frequency coefficients and a low frequency coefficient, a calculator which calculates the high frequency coefficients of the brightness signal and the color signals, generates a set of different high frequency coefficients, and produces a new brightness signal by adding the low frequency coefficient of the brightness signal to the set of different high frequency coefficients, and a reverse converter which performs a reverse frequency conversion operation on the new brightness signal.
The frequency conversion operation and the reverse frequency conversion operation may be in conformance to a Wavelet conversion method and produce a mono-chrome signal of a 2n-multiple resolution based on a color image signal wherein n is an integer having a value of zero or a negative integer such as xe2x88x921, xe2x88x922, and so on.
Further, to achieve the above-mentioned objects, a novel method for image processing which includes the steps of performing a frequency conversion operation on a color image signal which includes a brightness signal and color signals, dividing values of each of the brightness signal and the color signals into high frequency coefficients and a low frequency coefficient, calculating the high frequency coefficients of the brightness signal and the color signals, generating a set of different high frequency coefficients, producing a new brightness signal by adding the low frequency coefficient of the brightness signal to the set of different high frequency coefficients, and performing a reverse frequency conversion operation on the new brightness signal.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.